1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used as a transmission for a car or various industrial machines.
2. Description of the Related Art
As a transmission for a car, conventionally, there has been partially used such a toroidal-type continuously variable transmission as shown in FIGS. 19 and 20. In the present toroidal-type continuously variable transmission, for example, as disclosed in JP-A-62-71465U, an input side disk 2 serving as a first disk is supported concentrically with an input shaft 1 and, to the end portion of an output shaft 3 which is disposed concentrically with the input shaft 1, there is fixed an output side disk 4 serving as a second disk. In the interior of a casing in which the toroidal-type continuously variable transmission is stored, there are disposed trunnions 6, 6 which can be swung about their respective pivot shafts 5, 5 disposed at twisted position with respect to the input shaft 1 and output shaft 3, which do not intersect with the center axes of the input side and output side disks 2, 4 but exist in directions at right angles or almost at right angles to the directions of the center axes of the input side and output side disks 2, 4.
That is, each of the trunnions 6, 6 is structured such that, as shown in FIG. 21 and FIG. 23 (which will be discussed later), in the two end portions of the longitudinal direction (in FIGS. 21 and 23, in the right and left direction) of a support plate portion 7 of the trunnion 6, there are formed a pair of bent wall portions 8, 8 which are respectively bent toward the inner surface side (in FIG. 21, toward the upper side) of the support plate portion 7. And, by these bent wall portions 8, 8, there is defined a recess-shaped pocket portion P in which a power roller 11 (which will be discussed later) can be stored. Also, on the outer surfaces (the surfaces on the opposite side to the support plate portion 7) of the bent wall portions 8, 8, there are disposed pivot shafts 5, 5 in such a manner that they are concentric with each other.
A circular hole 10 is formed in the central portion of the support plate portion 7 and, the base end portion of a displacement shaft 9 is supported in the circular hole 10. And, by swinging the trunnions 6, 6 about their respective pivot shafts 5, 5, the inclination angle of the displacement shafts 9 supported on the central portions of the trunnions 6, 6 can be adjusted. Power rollers 11 are rotatably supported on the peripheries of the leading end portions of the displacement shafts 9 projected out from the inner surfaces of the respective trunnions 6, 6; and, the power rollers 11, 11 are respectively held by and between the input side and output side disks 2, 4. By the way, the base end portions and leading end portions of the respective displacement shafts 9, 9 are eccentric to each other.
Each of the sections of the mutually opposing inner surfaces 2a, 4a of the input side and output side disks 2, 4 has a concave surface which can be obtained by rotating an arc having the pivot shaft 5 as a center thereof or a curved line close to such arc. And, the peripheral surfaces 11a, 11a, which are respectively formed in a spherically convex surface, of the power rollers 11, 11 are contacted with their associated inner surfaces 2a, 4a of the input side and output side disks 2, 4
A pressing device 12 of a loading cam type is interposed between the input shaft 1 and input side disk 2. This pressing device 12 elastically presses the input side disk 2 toward the output side disk 4. Also, the pressing device 12 has a cam plate 13 which can be rotated together with the input shaft 1, and a plurality of (for example, four) rollers 15, 15 respectively held by a retainer 14. Further, on one side surface (in FIGS. 19 and 20, the left-side side surface) of the cam plate 13, there is formed a cam surface 16 which is a curved surface extending over the peripheral direction of the cam plate 13; and, on the outer surface (in FIGS. 19 and 20, the right-side side surface) of the input disk 2, there is formed a similar cam surface 17. And, the plurality of rollers 15, 15 are supported such that they can be rotated about an axis which extend in the radial direction with respect to the input shaft 1.
In the thus structured toroidal-type continuously variable transmission, in case where the input shaft 1 is rotated, the cam plate 13 is rotated with the rotation of the input shaft 1, the cam surface 16 presses the plurality of rollers 15, 15 against the cam surface 17 formed on the outer surface of the input side disk 2. As a result of this, the input side disk 2 is pressed by the plurality of power rollers 11, 11 and, at the same time, due to the mutual pressing operation between the pair of cam surfaces 16, 17 and the plurality of rollers 15, 15, the input side disk 2 is rotated. And, the rotational movement of the input side disk 2 is transmitted through the respective power rollers 11, 11 to the output side disk 4, thereby being able to rotate the output shaft 3 fixed to the output side disk 4.
When changing the rotation speed between the input shaft 1 and output shaft 3, specifically, when reducing the rotation speed between the input shaft 1 and output shaft 3, the trunnions 6, 6 are swung about their respective pivot shafts 5, 5 and the displacement shafts 9, 9 are inclined in such a manner that, the peripheral surfaces 11a, 11a of the power rollers 11, 11, as shown in FIG. 19, can be respectively contacted with the near-to-center portion of the inner surface 2a of the input side disk 2 and the near-to-outer-periphery portion of the inner surface 4a of the output side disk 4.
On the other hand, when increasing the rotation speed between the input shaft 1 and output shaft 3, the trunnions 6, 6 are swung and the displacement shafts 9, 9 are inclined in such a manner that, the peripheral surfaces 11a, 11a of the power rollers 11, 11, as shown in FIG. 20, can be respectively contacted with the near-to-outer-periphery portion of the inner surface 2a of the input side disk 2 and the near-to-center portion of the inner surface 4a of the output side disk 4. And, in case where the inclination angles of the displacement shafts 9, 9 are set intermediate between the angles in FIGS. 19 and 20, there can be obtained an intermediate transmission ratio between the input shaft 1 and output shaft 3.
Further, FIGS. 22 and 23 show a more specified version of the toroidal-type continuously variable transmission which is disclosed in JP-A-1-173552U. In this structure, the input side disk 2 and the output side disk 4 are respectively supported on the periphery of a circular-pipe-shaped input shaft 18 through their associated needle roller bearings 19, 19 in such a manner that they can be rotated as well as can be shifted in the axial direction thereof. Also, the cam plate 13, which is used to constitute the pressing device 12 of a loading cam type, is spline engaged with the outer peripheral surface of the end portion (in FIG. 22, the left end portion) of the input shaft 18, while the cam plate 13 is prevented from moving apart from the input side disk 2 by a flange portion 20. Further, an output gear 21 is connected to the output side disk 4 by keys 22, 22, while the output side disk 4 and output gear 4 can be rotated synchronously.
On the two end portions of each of a pair of trunnions 6, 6 each having such a structure as shown in the previously described FIG. 21, there are disposed pivot shafts 5, 5 respectively; and, these pivot shafts 5, 5 are supported in such a manner that they can be swung with respect to a pair of support plates 23, 23 and can be shifted in the axial direction thereof (in FIG. 22, in the front and back direction; and, in FIG. 23, in the right and left direction). That is, the pivot shafts 5, 5 are supported inside support holes 23a formed in the support plates 23, 23 by radial needle roller bearings 32.
And, in the circular holes 10 formed in the central portions of the support plate portions 7 which constitute their respective trunnions 6, 6, there are rotatably supported the base end portions 9a of displacement shafts 9 each structured such that the base end portion 9a and leading end portion 9b thereof are parallel to and eccentric to each other. Also, the power roller 11 is rotatably supported on the periphery of the leading end portion 9b of each of the displacement shafts 9 projected from the inner surfaces of their respective support plate portions 7.
By the way, the pair of displacement shafts 9, 9, which are disposed on each pair of trunnions 6, 6, are arranged at positions which are situated on the 180° opposite side to each other with respect to the input shaft 18. Also, a direction, in which the leading end portions 9b of the displacement shafts 9, 9 are eccentric to their respective base end portions 9a, is the same direction (in FIG. 23, in the right and left reversed direction) as the rotation direction of the input side and output side disks 2, 4. Also, this eccentric direction is a direction which intersect substantially at right angles to the direction in which the input shaft 18 is arranged. Therefore, the power rollers 11, 11 are supported in such a manner that they can be slightly shifted in the longitudinal direction of the input shaft 18. As a result of this, in case where the power rollers 11, 11 tend to shift in the axial direction of the input shaft 18 due to the elastic deformation of the respective component parts of the toroidal-type continuously variable transmission caused by a thrust load generated by the pressing device 12, an unreasonable force can be prevented from being applied to the respective component parts, so that the shifting movements of the power rollers 11, 11 can be absorbed.
Also, between the outer surfaces of the power rollers 11, 11 and the inner surfaces of the support plate portions 7 constituting the trunnions 6, 6, there are interposed thrust ball bearings 24 (which are thrust rolling bearings) and thrust needle roller bearings 25 in the order starting from the outer surfaces of the power rollers 11. Of these bearings, each of the thrust ball bearing 24, while supporting a thrust-direction load applied to each of the power rollers 11, allows the rotation of the present power roller 11. Each of the thrust ball bearing 24 includes a plurality of balls 26, 26, a circular-ring-shaped retainer 27 for holding the balls 26, 26 in a rollable manner, and a circular-ring-shaped outer race 28. Also, the inner race raceway of each of the thrust ball bearings 24 is formed in the outer surface of its associated power roller 11, while the outer race raceway of each of the thrust ball bearings 24 is formed in the inner surface of its associated outer race 28.
Also, the thrust needle roller bearings 25 are held by and between the inner surfaces of the support plate portions 7 constituting their respective trunnions 6, 6 and the outer surfaces of the associated outer races 28. The thus arranged thrust needle roller bearings 25, while supporting thrust loads applied from their respective power rollers 11 to the their respective outer races 28, allow these power rollers 11 and outer races 28 to be swung and shifted about the base end portions 9a of their respective displacement shafts 9.
Further, drive rods 29 are respectively connected to the one-end portions (in FIG. 23, the left end portions) of the trunnions 6, 6, while drive pistons 30 are respectively fixed to the outer peripheral surface in the intermediate portions of their associated drive rods 29. And, these drive pistons 30 are respectively inserted oil-tight into their associated drive cylinders 31.
In the case of the thus structured toroidal-type continuously variable transmission, the rotational movement of the input shaft 18 is transmitted through the pressing device 12 to the input side disk 2. And, the rotational motion of the input side disk 2 is transmitted through the pair of power rollers 11, 11 to the output side disk 4 and, further, the rotation power of the output side disk 4 is taken out by the output gear 21.
Now, when changing the rotation speed ratio between the input shaft 18 and output gear 21, the pair of drive pistons 30, 30 are shifted in the mutually opposite directions. As the pair of drive pistons 30, 30 are shifted in this manner, the pair of trunnions 6, 6 are shifted in the mutually opposite directions. For example, the power roller 11 situated on the lower side in FIG. 23 is shifted to the right in FIG. 23, whereas the power roller 11 situated on the upper side in FIG. 23 is shifted to the left in FIG. 23. This changes the direction of tangential-direction forces acting on the contact portions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4. And, due to such change of the direction of the tangential-direction forces, the trunnions 6, 6 are swung in the mutually opposite directions about their respective pivot shafts 5, 5 which are pivotally supported on the support plates 23, 23.
As a result of this, as shown in FIGS. 19 and 20 which have been previously discussed, the mutual contact positions between the peripheral surfaces 11a, 11a of the power rollers 11, 11 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4 are changed, which in turn changes the rotation speed ratio between the input shaft 18 and output gear 21. Also, in case where torque to be transmitted between the input shaft 18 and output gear 21 varies to thereby change the elastic deformation amounts of the respective component parts, the power rollers 11, 11 and outer races 28 belonging to these power rollers 11, 11 are slightly rotated about the base end portions 9a of their respective displacement shafts 9. Since, between the outer surfaces of the outer races 28 and the inner surfaces of the support plate portions 7 constituting the trunnions 6, there are interposed their associated thrust needle roller bearings 25, the above slight rotation can be attained smoothly. Therefore, as has been described before, there is required only a small force to change the inclination angles of the respective displacement shafts 9, 9.
When the above-described conventional toroidal-type continuously variable transmission is in operation, to the power rollers 11 which are rotatably supported on the inner surface side (pocket portion P side) of the respective trunnions 6, 6, there are applied thrust loads from the inner surfaces 2a, 4a of the input side and output side disks 2, 4. And, these thrust loads are transmitted through the thrust ball bearings 24 and thrust needle roller bearings 25 to the inner surfaces of the support plate portions 7 constituting the trunnions 6. Therefore, when the toroidal-type continuously variable transmission is in operation, the trunnions 6, 6, as shown exaggeratedly in FIG. 21, are elastically deformed although slightly in the direction where the inner surface sides of the trunnions 6, 6, where the power roller 11 are situated, can provide concave surfaces.
And, in case where such elastic deformation amount increases, the thrust loads applied to the balls 26, 26 which are rolling bodies constituting the thrust ball bearings 24 and the needle rollers constituting the thrust needle roller bearings 25 are made uneven. That is, as a result of the elastic deformation of the respective trunnions 6, the distances between the inner surfaces of the support plate portions 7 constituting the trunnions 6 and the outer surfaces of the power rollers 11 are made uneven. This reduces the thrust loads to be applied to the rolling bodies existing in the portion where the distance between these mating surfaces are increased, whereas this increases the thrust loads to be applied to the rolling bodies existing in the portion where the distance between these mating surfaces are reduced. As a result of this, an excessively large thrust load is applied to some of the rolling bodies to thereby increase excessively the contact pressures between the present rolling bodies and the raceway surfaces with which the rolling surfaces of the present rolling bodies are contacted, which shortens greatly the fatigue lives of these rolling surfaces and raceway surfaces.
Also, stresses are easy to concentrate on the connecting portion A (see FIG. 24) between the pivot shafts 5, 5 (which are disposed on the two end portions of each of the trunnion 6 and serve as the rolling surfaces of the incliningly rolling bearings) and the support plate portion 7 for supporting the power roller 11; and, therefore, in case where excessive torque is input to thereby elastically deform the trunnion 6 in the above-mentioned manner, the connecting portion A can be easily damaged, for example, it can be cracked. To avoid this, conventionally, the thickness of the trunnion 6 is increased to thereby prevent such damage. However, in this case, undesirably, the size of the trunnion 6 increases to thereby increase not only the weight thereof but also the cost thereof. Also, the pivot shafts 5 and support plate portions 7 must be connected together with a larger radius than necessary, which raises another problem when working them.
Also, in case where the trunnion 6 is elastically deformed in such a manner as shown in FIG. 21, the displacement shaft 9 is inclined with respect to the trunnion 6. In this case, stresses concentrate on the engaging portion B (see FIG. 24) between the base end portion 9a of the displacement shaft 9 and trunnion 6, so that the engaging portion B can be easily damaged, for example, cracked. Also, in case where the displacement shaft 9 is inclined with respect to the trunnion 6, the position of the power roller 11 supported on the leading end portion 9b of the displacement shaft 9 is shifted and the contact points between the peripheral surface 11a of the power roller 11 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4 are shifted from their respective given positions, thereby making the transmission operation unstable.